The effect on lymphocyte chromosomes of additional radiation burden due to fallout in Salzburg (Austria) from the Chernobyl accident.

An investigation has been carried out to determine whether chromosome aberrations in peripheral blood lymphocytes reflect the elevated environmental dose of low-LET ionising radiation, mainly due to radiocesium from Chernobyl fallout, to the population living in Salzburg city. Sixteen volunteers were sampled 1 year after the Chernobyl accident. Two of these persons were also sampled before the accident, and then in 1988 and 1990. The radioactive environment of Salzburg city and the radiation burden of its inhabitants have been frequently determined before and after the accident. The Cs-137 content of the volunteers was measured by whole-body counting. The additional external plus internal radiation doses in the year 1987 to the tested individuals ranged between 15 and 68% of the former normal environmental burden. The aberration frequencies showed a sharp increase of about a factor 6 from the pre-Chernobyl dose rate (0.9. mGy/year) to the post-Chernobyl dose rate (about 2 mGy/year total) but then decreased again with higher additional dose. In the two persons analysed before and up to 4 years after the accident the aberration yield showed a significant increase from 1984/85 to 1987, a decrease in 1988 and a further decrease in 1990. If these last 2 values are plotted against additional dose they fit the curve of the pooled 1987 values. The dose-effect curves revealed the same tendency as we found in various previous investigations and support the assumption that repair enzymes could be triggered by a certain amount of damage to the DNA.

Chromosomal damage induced in human lymphocytes by low doses of D-T neutrons.

Unstable chromosome aberrations induced by in vitro irradiation with zero plus seven low doses of 14.8 MeV D-T neutrons in the range 3.55-244 mGy have been analysed in human peripheral blood lymphocytes. In order to obtain the required large numbers of scored cells for such low doses, fourteen laboratories participated in the experiment. The dose responses for dicentrics, excess acentrics and total aberrations, fitted well to the Y = alpha D model. The alpha coefficient of yield for dicentrics, 1.60 +/- 0.07 X 10(-2) Gy-1, compares well with the values obtained in previous studies with D-T neutrons at somewhat higher doses. Results from a previous collaborative study using 250 kVp X-rays over a comparable dose range indicated the possible existence of a threshold below 50 mGy. In the present study there is no clear evidence for neutrons for such a threshold. However, the data were insufficient to permit the rejection of a possible threshold below approximately 10 mGy.

Effect of low-dose acute X-irradiation on the frequencies of chromosomal aberrations in human peripheral lymphocytes in vitro.

In a coordinated research programme sponsored by the International Atomic Energy Agency, the frequencies of chromosomal aberrations induced in peripheral blood lymphocytes (in vitro) by 250 kV X-rays at low doses (0.4, 1, 2, 3, 5, 10 and 30 rad) were determined. Blood from 2 donors was used to conduct one master experiment at these dose levels. The culture time used was 48 h and all samples including the controls were processed according to a standard protocol. The coded slides were scored by investigators from 10 participating laboratories. The main results are the following: (1) the frequencies of all types of chromosome aberrations at 0.4 rad are significantly lower than the control values; (2) there is no increase in the frequencies of dicentrics up to 2 rad and in those of terminal deletions up to 5 rad; (3) the mean frequencies of all aberrations considered together are not significantly different from one another at 1, 2 and 3 rad (P = 0.05); and (4) over the entire dose range the dose-effect relationship is clearly non-linear. A fit of these data to a linear quadratic model (E(D) = c + alpha D + beta D2) showed that the observed total aberration frequencies at doses 1, 2, 3 and 5 rad are below the curve defined by the model. The deviations can be explained by an altered kinetics of aberration production at very low doses probably due to DNA repair mechanisms operating these cells.

Chromosomal aberrations of blood lymphocytes induced in vitro by radon-222 daughter alpha-irradiation.

Blood samples were irradiated in vitro with alpha-rays emitted from short-lived radon decay products dissolved in the culture medium at doses between 0.03 and 41.4 mGy. The data were collected from experiments conducted during the period 1984-1992 and comprise a total of about 64000 scored metaphases. For statistical reasons, only 60,022 metaphases were used for the subsequent analysis. The results for total chromosome aberrations and dicentrics indicate a linear dose dependence in the dose range above about 10 mGy, consistent with other experimental observations. At doses below about 10 mGy, aberration frequencies cannot be linearly extrapolated from higher doses, suggesting that there is no dependence on dose within a certain low-dose range. In addition, a statistically significant minimum has been observed at a dose of about 0.03 mGy, which is consistently lower than the related control values. The behavior of the aberration frequencies in the low-dose region seems to be influenced by the control values, which also depend on the environmental radiation burdens to the donors before blood sampling and thus were significantly affected by the Chernobyl fallout.

Evaluation of radiation-induced chromosomal aberrations in human peripheral blood lymphocytes in vitro: result of an IAEA-coordinated programme.

The results of an IAEA coordinated programme on radiation induced chromosomal aberrations in human peripheral blood lymphocytes in vitro are presented. In a master experiment, a whole blood sample from one donor was irradiated with 200 R of X-rays. Different fixation times from 46 to 82 h were used. The progression of cells into mitosis was monitored by BrdUrd incorporation. 14 investigators took part in the scoring of chromosomal aberrations. The main conclusions of this study are: (1) The mean frequencies of aberrations changed with fixation time. (2) The number of cells scored as aberrant by different laboratories was very similar, but there was variability in the number of aberrations scored per aberrant cell. (3) The differences in the frequencies of aberrations between laboratories were minimal when the scoring was restricted to the first major peak of mitotic activity and sufficient cells were scored. It is concluded that using controlled experimentals conditions, human peripheral blood lymphocytes can effectively be used as a reliable biological dosimeter for absorbed radiation dose.

Radiation exposure of the respiratory tract and associated carcinogenic risk due to inhaled radon daughters.

The atmospheric content of radon and its decay products contributes significantly to the radiation exposure of man even in the normal environment. In this study, the risk for lung cancer induction associated with normal exposure to natural radionuclides is assessed in Salzburg, Austria. Altogether more than a thousand rooms have been investigated by using combined radon grab-sampling methods together with continuous measurements of radon and daughters at different control stations. Dose calculations were carried out for 729 demoscopically selected test persons, considering individual differences in age, sex and life-style and atmospheric nuclide concentrations at different sites. Using a specially developed age-dependent lung model, the dose frequency distribution of the absorbed dose to the basal cells of the bronchial epithelium could be evaluated for the population of Salzburg. Dose modifications caused by anatomical and physiological variabilities as well as microdosimetric considerations of the stochastic events during energy deposition result in a significantly increased dispersion of the dose histogram. Induction of lung cancer due to inhalation of radon and decay products can be correlated with cumulative exposure based on experience with lung cancer incidence amongst uranium miners. Using the recommended range of lifetime risk values of 20-45 X 10(-5)/WLM (UN77), it is shown for Salzburg that about 15% of the observed number of lung cancer cases may be induced by natural radionuclides.

Relationship between the 210Pb content of teeth and exposure to Rn and Rn daughters.

Existing data on 210Pb in human teeth are reviewed for various countries. The mean value of 210Pb in the teeth of population groups exposed to "normal" levels of radon-daughter exposure is about 2 mBq/g. A detailed analysis of 48 samples from a "normal" Italian population group revealed that smoking habits and age may have some influence on 210Pb content of teeth, while this is not the case for differences in sex. A group of 45 Austrians exposed to elevated levels of radon and radon daughters is compared with the Italian group. After subtraction of background levels of 210Pb as found for the normal Italian population, the incremental 210Pb tooth content due to excessive radon-daughter exposure has been correlated with the individual cumulative exposure corrected for background radon-daughter exposure. A statistical analysis shows the significance of the linear correlation at the alpha = 0.01 level. For the incremental increase of 210Pb in teeth, a value of 1.2 mBq/g has been used for a lifetime exposure to 1 WLM. This result is compared to corresponding data published in the literature, which are predominantly related to the 210Pb content of bone after short-time exposure at high levels, e.g. in uranium mines. The comparison seems to indicate the influence of the exposure rate and the need for a comprehensive model, which takes into account radon-daughter inhalation, radon dissolved in body fluids and 210Pb metabolism.

The Chernobyl fallout in Salzburg/Austria and its effect on blood chromosomes.

The radioactive fallout of the Chernobyl accident caused an increase in radiation dose of 20 to 110 per cent over the normal environmental burden to the inhabitans of Salzburg City in Austria (in a distance of about 1300 km from the accident). The structural chromosome aberration in the lymphocytes of the peripheral blood of 15 test-persons have been investigated one year after the accident. From two of these we know also the aberration frequencies before the accident which were significantly lower. The results from all test persons were pooled according to their Cs137 and Cs134 content, measured by whole body counter. Their mean additional blood doses from the incorporated caesium plus the external fallout radiation were 0.23, 0.36 and 0.55 mGy/yr. The aberration frequencies increased with dose. The slope of the best straight-line through the points was 2.0 +/- 0.7 total chromosome type aberrations in 100 metaphases per mGy/yr. This result fits in well with former investigations of persons with individually calculated radiation burden from the environment. The sharp increase with dose at this low level is not compatible with values extrapolated from high doses. The usual dose assessment based on chromosome aberrations extrapolated from high to low doses is therefore not possible in the range considered in this investigation.

Cytogenetic effects of chemotherapy and cranial irradiation on the peripheral blood lymphocytes of children with malignant disease.

Results of a cytogenetic analysis of peripheral blood lymphocytes of children with leukemia after massive chemotherapy and cranial irradiation, and of children with nephrosis after coritisone therapy and cyclophosphamide are presented. Prolonged intensive chemotherapy results in a significant rise in the number of chromatid aberrations after twelve months, and of chromosomal aberrations after 24 months of therapy. After cranial irradiation a sharp rise in chromosome aberrations is present for about three months. This drops after one year to levels present in cases with chemotherapy alone.